The transfer roll has long been used in the printing industry to transfer a specified amount of ink or other, usually liquid, medium from the fountain roll to the print roll or material being printed. The quantity of ink transfered to the print roll or material to be coated is the amount contained within the pores or irregularities in the roll surface.
The history of the transfer roll is long and marked by many attempts at producing a long-wearing, corrosion resistant transfer roll capable of accurately metering desired quantities of ink. Early transfer rolls were made of soft metal which would be deformed by a knurling tool to form ink holes. These holes were generally hemispherical or pyramidal shaped to help the roll withstand the crushing force imparted by the doctoring system. In practice, the transfer roll usually runs against a doctor blade (either in a reverse or forward position) on a fountain roll. The doctor blade is made of hard, wear-resistant metal. The pressure of the doctor blade upon the soft metal transfer roll has a tendency to crush the ink holes and otherwise cause severe abrasions on the transfer roll surface. Ink transfer rolls having a soft metal surface with kurled or engraved holes for receiving ink are also very susceptible to damage from corrosive inks. Examples of such ink transfer rollers are illustrated in U.S. Pat. No. 2,393,529 which issued Jan. 22, 1946, to Harrigan and U.S. Pat. No. 2,638,050 which issued May 12, 1953, to King.
The ceramic transfer roll was developed in an attempt to improve the wear-resistance of the ink transfer roll. The first generation ceramic roll plasma coated a metal core with ceramic and either left the roll in the as sprayed configuration or ground the surface to a specific surface finish. In those cases where after grinding the surface was too smooth to do any metering, it was lightly grit blasted. In general, the inherent surface irregularities of the ceramic coating of the first generation ceramic roll provided the ink transfer surface. However, such ceramic rolls metered ink poorly and unevenly. Further, the exact lay-down or carrying capacity was difficult or impossible to duplicate. Also the rough textured surface of the rolls wore mating equipment more quickly. Examples of such ceramic coated transfer rolls are illustrated in British Pat. No. 1,407,079 published Sept. 24, 1975, based upon the application of Hans Schwoepfinger, as well as Canadian Pat. No. 1,009,507 which issued May 3, 1977, to Haye.
Further attempts to improve the ink transfer roll resulted in the second generation ceramic roll which was a mechanically engraved roll coated with ceramic. That is, the metal core of relatively soft metal material was knurled or engraved in the conventional manner to produce uniform ink holes of the hemishperical or pyramidal configuration. The engraved roller was then coated with a very thin ceramic layer. The ceramic necessarily had to be very thin for a build up of ceramic would fill the ink holes rendering the surface too smooth for ink transfer. While the second generation ceramic roll better metered ink than the first generation ceramic roll, most of the disadvantages of the first generation ceramic roll remained with the second generation ceramic roll. The second generation roll like the first generation roll had a rough textured surface making the mating equipment wear rapidly. The relatively thin ceramic coating rendered the ink transfer roll only slightly more damage resistant than the previously known metal rolls such as the prior art rolls described hereinbefore, and the prior art metal rolls which utilized a hard corrosion resistant metal surface over the soft metal core to assist in extending the roll life. In that the technique for forming the ink holes remained the same as that used in the very early rolls with knurled or engraved holes, these inking rolls were limited to the same degree as the early metal rolls in the number of the ink holes per line that could be formed. An example of the metal roll with a hard corrosion resistant metal surface is illustrated in U.S. Pat. No. 2,208,068 to Byle et al. This patent issued Oct. 13, 1959. Examples of the second generation ceramic roll are illustrated in U.S. Pat. No. 4,009,658 to Heurich which issued Mar. 1, 1977, and British Pat. No. 1,585,143 published Feb. 25, 1981 on the application of Pamarco Incorporated.
In each of the aforementioned references where ink holes were formed in the roll surface and the inherent roughness of the roll surface was not used for storing ink, a mechanical knurling or engraving is used. In U.S. Pat. No. 3,985,953 to Dunkley which issued Oct. 12, 1976, a gravure printing member made of a plastic material is provided with inking holes through the use of a continuous wave scanning laser beam or other energy beam.
There exists the need for an ink transfer roll with a hard surface such as that provided by a ceramic surface which exhibits a smooth mating surface to the mating equipment and which can meter the ink accurately while providing extremely fine line counts. If the surface of the roll is too coarse, excessive ink will be transfered to the print roll or material and hence a blotchy, smeared print will result. If the finish of the roll is too smooth, a light or skip pattern would appear in the printed work. If the transfer roll surface was not significantly damage resistant it would be scraped, gouged or scratched to produce a roll surface which would cause blobs of ink to transfer to the printing. Such problems exist with the known transfer roll.